Method and apparatus for controlling specific gravity in a heavy medium process



plml 26., N966 p, w, CHASE ET AL METHOD AND APPARATUS FOR CONTROLLING SPECIFI GRAVITY IN A HEAVY MEDIUM PROCESS Filed Nov. l5, 1962 2 Sheets-Sheetl l /W//VERAL PART/CLES WA TEE' 'v' CUNCEN TR TE /NvE/a/roRs. PAUL N. CHASE and ALBERT T. No5/VEN @y P. W. CHASE ETAL GRAVITY IN A HEAVY MEDIUM PROCESS METHOD AND APPARATUS FOR CONTROLLING SPECIFIC April 26. 1966 Filed Nov. 13, 1962 2 W 4 A 5 D C C U CA Nl MR mUMR 7 8 0E SNTE R GAF Zu/l 2J FU. MADH .n L0 PMAs 1|. Am MN MM50 /0 .r Sc 6 3 ,l1/111 N 5 W. 3

9 3 1 n Mw v 5 @ma T R SDP NE a MN 1 wnw AW SDF INVENTORS. PAUL W. CHASE and ALBERT I KOE/VEN By WM Aitor/ley SUSPENSION RETURNED T0 PUMP BOX l0 United States Patent O 3,247,961 METHOD AND APPARATUS FOR CONTROL- LlNG SPECllFlC GRAVITY 1N A HEAVY ME- BEUM PRCESS Paul W. Chase, Mountain fron, and Albert T. Koenen,

Hibbing, Minn., assignors to United States Steel Corporation, a corporation of New Jersey Filed Nov. 13, 1962, Ser. No. 236,946 3 Claims. (Cl. 209-12.)

This invention relates to an improved method and apparatus for controlling specific gravity in a heavy medium minerals separation process.

In a conventional heavy medium process, mineral particles are introduced to a vessel which contains a mediu-m of specific gravity intermediate that of the values and gangue in the mineral. Commonly, the medium is a water suspension of a finely divided magnetic substance, :such as ferrosilicon or magnetite. If the mineral is an ore, such as iron ore, the values sink 4while the gangue oats. The reverse occurs with some materials, such as coal. After the sink and oat products leave the separating vessel, the suspension is drained therefrom and recovered for re-use. Next, the sink and float products a-re Washed. The wash water, along with a fraction of the suspension drained from the products, goes to a magnetic separator `and thence to a densiiier. The magnetic separator removes nonmagnetic contaminants and the densier removes water to produce a densied mediu-m of higher specific gravity than that use .in the separating vessel. This densied medium joins the remainder of the drained suspension and returns to the separa-ting vessel. Water accompanying the mineral particles dilutes the medium in the vessel to the proper specific gravity. Reference can be made to Wade Reissue Patent No. 22,191, dated September 29, 1942, for a detailed showing of a process of this type, although the specic pieces of equipment Wade shows are not of the most modern construction.

To achieve a maximum recovery of the values at the desired grade, the specific gravity of the medium in the separating vessel must be maintained uniformly at a substantially constant value. The usual practice has been for the operator to check the specific gravity of samples of the medium at intervals by manu-al means, and make any necessary adjustments after each check. Variation-s in the feed rate, Water content of the feed, and densifying characteristics make it diicult to exercise effective control by this procedure. C-hase and Hendrickson application Serial No. 236,944, led the same date as the present application discloses and claims an improved automatic method and apparatus for controlling specific gravity of the medium. One feature of the Chase and Hendrickson invention is that they vary the speedl of their densifier screw to effect a quick but temporary change in the rate at which densifier medium feeds back into the system. The present invention concerns an improvement over this feature.

An object of the present invention is to provide an improved method and apparatus for controlling the rate Iat which densifed medium feeds from a densifer into other parts of a heavy medium system.

A more speci-fic object is to provide an improved method and apparatus for controlling the feed rate from a densifier in which the densilier operates at constant speed and the feed rate is controlled by a splitter adjusted to return a variable fraction of the densier output back to the densier. l

ICC

In the drawings:

FIGURE 1 is a schematic flowsheet of a heavy medium minerals separation plant equipped with our improved apparatus for controlling the rate at which medium feeds from the densitie-r;

FIGURE 2 is a schematic wi-ring diagram of the circuit which controls the height of the densier screw; and

FIGURE 3 is a perspective view of a preferred form of splitter embodied in our apparatus.

Flowsheet FIGURE l shows a flowsheet of a heavy medium plant which includes a pump box 10, a medium-circulating pump 12, a separating vessel 13, and sink and float screens 14 and 15. Pump 12 continuously feeds the medium,

4 a Water suspension of magnetic particles, from the pump box 10 to the separating vessel 13. Mineral particles (for example 1% x 1/4 inch iron ore) also are introduced to this vessel. Heavier mineral particles sink in the medium and discharge from the sepa-rating vessel to the sink screen 14, While lighter mineral particles oat and discharge to the float screen 15. Screens 14 and 1'5 have drain sections 14a and 15a and wash sections .14b and 15b over which the sink and float products pass in succession. Suspension drained from the sink product as it passes over the drain section 14a return directly to the pump box 10. Suspension drained from 4the float product as it passes over the drain section 15a goes to an adjustable splitter 16, which routes variable fractions to the pump box 10 and to another pump box 17. Water is applied to both the sink and float products as they pass over the wash sections 14h and 15b to wash away additional medium. Wash Water from both products goes to the pump box 17, from which a pump 18 delivers the contents to a mangetic separator 19 to remove nonmagnetic contaminants. The remaining magnetic particles and Water go to a densier 20, which removes water. Densilied suspension from the densilier returns to the pump box 10. In the example of an ore, sink particles leaving screen 14 usually are a finished concentrate product, while float particles leaving screen 1S and nonni-agnetic contaminants lfrom the magnetic separator L19 usually are a finished tailing product.

The individual pieces of apparatus other than our preferred splitter, as well as the portion of the flowsheet t-hus far described, are'conventional and hence not described in greater detail. However, we point out that the densiier is of a type in which the depth of the rake can be changed to increase or decrease the quantity of densitied suspension feeding therefrom. We have illustrated a densitier which has a rotating rake or screw 21 and a motor 22 for lowering or raising the screw. A densier of this type, and also a suitable separating vessel and pumps, are available commercially from Western Machinery Co., San Francisco, California, and are described in a printed publication by the supplier entitled, Wemco Equipment for Heavy Media Separation, Bulletin No. Hl-Bl2 Another example of a suitable densiiier is a reciprocating rake type of classifier available commercially from Dorr- Oliver Incorporated, Stamford, Connecticut, and is described in a printed publication by the supplier, Bulletin 2281. We also point out that the plant may include other conventional pieces of apparatus, such as demagnetizing coils for the recovered suspension, which we have not shown, since they are not involved in the present invention.

As in the invention disclosed in the aforementioned Chase and Hendrickson application, we mount a density meter 23 at a convenient place in the owsheet, illustrated in the line which carries medium from pump 12 to the separating vessel 13, and we connect a specific gravity recorder 25 to this meter. The specic gravity of the lmedium carried in this line is a little higher than that of the medium in the vessel, but it may be considered representativey for control purposes. In accordance with our invention, we interpose a second adjustable splitter 26 between the densier 20 and pump box 10. Densied suspension from the densitier goes to this second splitter, which transfers only a variable fraction of this suspension to the pump box 10 and returns the remainder to the densifier. In the arrangement illustrated, the recordercontroller 25 transmits a signal representative of the density of the medium in Vessel 13 to a splitter-positioner 27, which is mechanically connected to splitter 26. The positioner 27 adjusts the splitter to vary the fraction of the densied suspension transferred to the pump box inversely with changes in specic gravity. If the Specic gravity orf the medium entering vessel 13 goes down from its set value, splitter 26 transfers a larger fraction of the densied suspension to the pump box 10. The reverse action occurs if the specic gravity goes up from its set value.

After an adjustment is made in the position of splitter 26, there is an immediate change in the level of medium in the pump box 10. If a larger or smaller fraction of the densied suspension goes to the pump box, the level rises or falls. We connect a level-sensing device 29 to the pump box and connect a controller 30 to the level-sensing device. Controller- 30 transmits a signal representative of the level of medium in the pump box to a splitter-positioner 31, which is mechanically connected to splitter 16. When the level rises or falls, the positioner 31 adjusts splitter 16 to restore the level to its set value. That is, 'if the level in the pump box rises from its set value, the splitter routes a larger fraction of the drained suspension to the magnetic separator 19 and densifer 20 and a smaller fraction directly to the pump box 10. Thus the net effect of a decrease in specic gravity from the set value is that a larger quantity of densied suspension goes to the pump box 10 and a larger quantity of drained suspension goes to the magnetic separator 19 and densiier 20. The net effect of an increase in specific gravity from the set value is the reverse. In either event the system stabilizes when the medium reaches a specific gravity substanti-ally equal to a set value.

As the plant operates, the medium particles gradually are depleted. Hence the trend is for splitter 26 to transfer a larger and larger fraction of the densied suspension to the pump box 10 and return less to the densifier. We connect the splitter-positioner 27 with the raise-lower motor 22. When splitter 26 approaches its e-xtreme positions, in which it is transferring almost all or almost none of the densied suspension to the pump box, a signal for a further increase or decrease operates motor 22 to lower or raise the densitier screw 21.

Electric circuit FIGURE 2 is a schematic wiring diagram of one form of circuit we can use for operating the raise-lower motor 22. The circuit includes lines L1 and L2 connected to a suitable power source, and two timers T1 and T2. Timer T1 controls the length of time motor 22 runs each time it 'is energized, and timer T2 the interval which must elapse before motor 22 can run again after it once runs. Timer T1 operates with a maintained contact control switch and we set it to time out after a relatively brief period (for example 8 seconds). Timer T2 operates with a momentary contact control switch and wer set it to time out after a longer period (for example l minutes). Timer T2 has a normally closed Contact 35 and a doublethrow contact 36 which are connected internally. We connect line L1 with contact 35. We connect one end of the coils of two parallel latch-type relays A and B to cont-act 36 through normally open switches 37 and 38 respectively and connect the other end of each coil to line L2. As long as timer T2 is in its off or reset position, contact 35 is closed `and contact 36 positioned to connect the relay coils with line L1. Switch 37 closes when splitter 26 reaches a position in which it is transferring almost all the densied suspension from the densier 20 to the pump box 10. Switch 38 closes when the splitter is returning almost all the densied suspension to the densiier. When switch 37 or 38 closes, relay A or B is energized, provided sufficient time has elapsed since the previous operation for timer T2 to have reset. Relay A has normally open contacts A1 and A2 and relay B normally open contacts B1 and B2. Whenever either relay is energized, its contacts remain closed even though switch 37 or 38 may open, since the relays are of the latch-type.

We connect the timing circuit of Timer T1 across contact 36 of Timer T2 and line L2 in series with contact A1 or B1, whereby timer T1 is energized and commences to time when either contact A1 or B1 closes. Timer T1 has a normally open contact 39 and a double-throw contact 40 which are internally connected. We connect line L1 with contact 40 and connect one end of the coils of lower and raise relays 22a and 22b with contact 39 via contacts A2 and B2, respectively. We connect the other ends of the relay coils with Line L2. As soon as timer T1 is energized, contact 39 closes. As long as the timer is in its reset position or while it is timing, contact 40 is positioned to connect contact 39 with line L1. Thus whenever relay A is in latch position, relay 22a is energized via contacts 40, 39 and A2 to operate motor 22 in a direction to lower the densier screw 21. Similarly whenever relay B is in latch position, relay 22b is energized via contacts 40, 39 and B2 to operate motor 22 in the other direction to raise the screw.

We connect the timing circuit of timer T2 across contact 40 of timer T1 and line L2. When-timer T1 times out, contact 40 moves to a position to disconnect and deenergize relay 22a or 22b and to connect timer T2 with line L1, whereupon timer T2 is energized and commences to time. As soon as timer T2 is energized, contact 36 moves to its other position. We connect parallel reset coils 41 and 42 for relays A and B across contact 36 and line L2, whereby thesey coils are energized when contact 36 changes position. The normally open contacts of relay A or B open, whereupon timer T1 is deenergized and resets to the position shown in FIGURE 2. Timer T2 continues to run, since it operates with a momentary contact from timer T1. When timer T2 times out, contact 35 momentarily opens and deenergizes the reset coils 41 and 42. Finally timer T2 resets automatically to the position shown in FIGURE 2, whereupon the cycle can repeat whenever switch 37 or 38 closes.

Preferably the circuit to relays 22a and 22b includes a manual-automatic selector switch 43 and push buttons 44 and 44a for lowering or raising the densicr screw under manual operation. The circuit can also include limit switches 45 and 45a which open when the screw reaches its extreme positions to prevent further operation of motor 22.

Splitter FIGURE 3 shows structural details of our preferred form of splitter 16. A first fixed launder 46 receives suspension drained from the loat product on screen 15. A second fixed launder 47 is located beneath launder 46 to receive the fraction of the suspension which returns directly to the pump box 10. A third xed launder 48 is located beneath launder 46 and offset therefrom to receive the fraction which goes to the magnetic separator 19 and densitier 20. The splitter includes a swinging launder 49 and a pair of links 50 attached to this launder and pivoted to an overhead support 51. The swinging p launder is located in the space between the fixed launders 46 and-47 and it has an output spout 52 in its end above the fixed launder 48.- The positioner 31 is connected to the links 50 to move the swinging launder back and forth in .response to signals from the recorder-controller 25. Splitter 26 is of similar construction; hence we have not repeated the description. The splitter construction per se is claimed in another application filed by Luther G. Hendrickson, Serial No. 361,498, filed April 21, 1964, which is a division of application Serial No. 208,757, filed July 10, 1962.

Instruments The individual instruments used in our control appa- -ratus are of conventional construction and available commercially. lHence we have not shown nor described them in detail, but instead reference can be made to printed publications for showings.

`Considine, Process Instruments and Controls Handbook, published by McGraw-Hill Book Company, copyright 1957, Library of Congress Catalog` Card No.`

56-8169, shows and describes suitable instruments for several of our purposes. Considine shows a recordercontroller (page 11-22 or 11-26) suitable for our recorder-controller 25, and a cylinder-type operator with positioner (page -37) suitable for our splitter positioners 27 and 31. A suitable recorder-controller 2S also is available commercially from Leeds and Northrup Cmpany, Philadelphia, Pa., as Type H with CAT controller, and is described in printed publications by the supplier, Dia-tia Sheets ND46-33(106)80558 and ND46-5l(l00)60-65S and Folder ND4(7b)80- 1158, pages 9 and 10. A suitable positioner is available commercially from Foxboro Company, Foxboro, Mass., as the Stabiload, and -is `described in a printed publication by the supplier, Bulletin No. 446. Our density meter 23 can be an Ohmart Cell, as shown in Ohmart Patent No. 2,763,790, or a gamma gage. A suitable level sensing device 29 and level controller 30 are available commercially from Fisher Governor Company, Marshalltown, Iowa, as Type 24913 and Type 2500 Fisher Level- Trol and are described in a printed publication by the supplier., Data Sheets "ND4633(106)80558 and available commercial from Eagle Signal Co., Moline, Ill. as the Cycl-Flex reset timer and are described in a printed publicat-ion by the supplier, Bulletin 120, August 1955. Our illustrative recorder-controller generates an electric signal, which We use to control a pneumatically operated positioner 27. A suitable transducer for converting electric signals from the recorder to pneumatic pressure signals is available commercially from Fisher Governor Co. as Type 543 and is described in a printed publication -by the supplier, Bulletin E543.

From the foregoing description it is seen our invention affords a relatively simple yet effective method and apparatus for controlling the specic gravity of the medium used in a heavy medium minerals separation process.

We avoid any need to vary the speed of the densiier screw, as shown in other applications herein discussed. It is apparent also that the connections between the controllers 25 and 30 and the splitter-positioners 27 and 31 could be interchanged after the fashion of the modification shown in FIGURE 1 of the aforementioned Chase and Hendrickson application. In this event the specific gravity recorder-controller 2S would operate the splitterpositioner 31 through a suitable electric-to-pneumatic transducer, and the level controller would operate the splitter positioner 27 directly. We can also use our invention in conjunction with a cleanness control as shown in another Chase and Hendrickson application Serial No. 236,945, filed the same date as the present application. As long as the cleanness control is not used, we avoid introducing water to the separating vessel for control purposes.

While We have shown and described only a single embodiment of the invention, it is apparent that modifications may arise. Therefore, we do not wish to be limited to the disclosure set forth but only by the scope of the appended claims.

We claim:

1. In a heavy medium minerals separation process -in which mineral particles are introduced to a water suspension of magnetic particles, heavier mineral particles sink in the suspension while lighter mineral particles float, the .resulting sink and float products are successively drained of suspension and washed with water, both the wash water and a variable fraction of the drained suspension are treated in a magnetic separator and a densifier to remove nonmagnet-ic contaminants and water and thereby produce a densified suspension, said desied suspension together with the remainder of the drained suspension is transferred from the densifier to a pump box, and the suspension feeds from the pump box to a vessel Where the mineral particles are introduced, the combination therewith of a method of controlling the specific vgravity of the suspension in the vessel to a set value comprising measuring a specific gravity representat-ive of the suspension in the vessel, splitting the iiow of said densified suspension from the densifier to transfer only a variable fraction thereof to the pump box and return the remainder to the densier, adjusting the magnitude of the fraction transferred to the pump box in response to the specific gravity measurement to transfer more and raise the level in the pump box when the specific gravity goes down from said set value and transfer less and lower the level in the pump box when the specific gravity goes up, measuring changes in the level of suspension -in the pump box from a set level, and adjusting the magnitude of said fraction of drained suspension treated in the magnetic separator and densitier to increase the fraction as the level rises and decrease the fraction as the level falls and thereby restore the level in the pump box to said set level.

2. In a heavy medium minerals separation plant, which includes a separating vessel adapted to contain a water suspension of magnetic particles in Wh-ich heavier mineral sinks while lighter mineral particles tioat, means for successively draining the suspension from the sink and float products from said vessel and washing the products with water, a magnetic separator and a densifier, a first adjustable splitter for routing a variable fraction of the.drained suspension to said magnetic separator and densier along with the wash water to remove nonmagnetic contaminants and water and thereby produce a dens-itied suspension,

a pump lbox to which are transferred said densiied suspension from said densifier and the remainder of the drained suspension from said first splitter, and a pump yfor feeding the combined densied and drained suspension from sa-id pump box to said vessel, the combination therewith of an apparatus for controll-ing the specific gravity of the suspension in said vessel to a set value comprising means for measuring a specific gravity representative of the suspension in said vessel, means for measuring changes in the level of suspension in said pump box from a set level, a second adjustable' splitter for splitting the flow of said densilied suspension from said densier to transfer only a variable fraction threeof to said pump box and return the remainder to said densifier, means operatively connecting said specific gravity-measuring `means with one of said splitters, and means operatively connecting the level-measuring means with the other of said splitters, said connecting means adjusting said splitters to vary the magnitudes both of the treated fraction of the densied suspens-ion and of the fraction of the drained suspension treated in the magnetic separator and densitier to transfer and treat larger fractions as the speciiic gravity goes down from said set value and smaller fractions as the specific gravity goes up, with the adjustments taking 7 specic gravitymeasuring means adjusts the fraction of the densied suspension transferred to said pump box, and said level-measuring means adjusts the fraction of the drained suspension treated in said magnetic separator and densier.

References Cited by the Examiner UNITED STATES PATENTS 8 FOREIGN PATENTS 7/ 1956 Great Britain.

OTHER REFERENCES HARRY B. THORNTON, Primary Examiner.

HERBERT L. MARTIN, Examiner. 

1. IN A HEAVY MEDIUM MINERALS SEPARATION PROCESS IN WHICH MINERAL PARTICLES ARE INTRODUCED TO A WATER SUSPENSION OF MAGNETIC PARTICLES, HEAVIER MINERAL PARTICLES SINK IN THE SUSPENSION WHILE LIGHTER MINERAL PARTICLES FLOAT, THE RESULTING SINK AND FLOAT PRODUCTS ARE SUCCESSIVELY DRAINED OF SUSPENSION AND WASHED WITH WATER, BOTH THE WASH WATER AND A VARIABLE FRACTION OF THE DRAINED SUSPENSION ARE TREATED IN A MAGNETIC SEPARATOR AND A DENSIFIER TO REMOVE NONMAGNETIC CONTAMINANTS AND WATER AND THEREBY PRODUCE A DENSIFIED SUSPENSION, SAID DENSIFIED PENSION TOGETHER WITH THE REMAINDER OF THE DRAINED SUSPENSION IS TRANSFERRED FROM THE DENSIFIER TO A PUMP BOX, AND THE SUSPENSION FEEDS FROM THE PUMP BOX TO A VESSEL WHERE THE MINERAL PARTICLES ARE INTRODUCED, THE COMBINATION THEREWITH OF A METHOD OF CONTROLLING THE SPECIFIC GRAVITY OF THE SUSPENSION IN THE VESSEL TO A SET VALUE COMPRISING MEASURING A SPECIFIC GRAVITY REPRESENTATIVE OF THE SUSPENSION IN THE VESSEL, SPLITTING THE FLOW OF SAID DENSIFIED SUSPENSION FROM THE DENSIFIER TO TRANSFER ONLY A VARIABLE FRACTION THEREOF TO THE PUMP BOX AND RETURN THE REMAINDER TO THE DENSIFIER, ADJUSTING THE MAGNITUDE OF THE FRACTION TRANSFERRED TO THE PUMP BOX IN RESPONSE TO THE SPECIFIC GRAVITY MEASUREMENT TO TRANSFER MORE AND RAISE THE LEVEL IN THE PUMP BOX WHEN THE SPECIFIC GRAVITY GOES DOWN FROM SAID SET VALUE AND TRANSFER LESS AND LOWER THE LEVEL IN THE PUMP BOX WHEN THE SPECIFIC GRAVITY GOES UP, MEASURING CHANGES IN THE LEVEL OF SUSPENSION IN THE PUMP BOX FROM A SET LEVEL, AND ADJUSTING THE MAGNITUDE OF SAID FRACTION OF DRAINED SUSPENSION TREATED IN THE MAGNETIC SEPARATOR AND DENSIFIER TO INCREASE THE FRACTION AS THE LEVEL RISES AND DECREASE THE FRACTION AS THE LEVEL FALLS AND THEREBY RESTORE THE LEVEL IN THE PUMP BOX TO SAID SET LEVEL. 